Garlic is a bulbous plant belonging to the genus Allium, and is a very popular seasoning. Garlic has also been used as a folk medicine for diseases such as arteriosclerosis, pulmonary tuberculosis and bronchitis, and as an antimicrobial agent and vermicide. It is believed that the major causal substances providing these medicinal effects of garlic are allicin, ajoene and other sulfur-containing organic compounds. Block et al. (J. American Chem. Soc. 106, P8295-8296, 1984) reported that ajoene, one of the sulfur-containing medicinal substances obtained from garlic, inhibits platelet aggregation and is prepared by incubating chopped garlic in methyl alcohol.
The mechanism of the platelet aggregation inhibition of ajoene was studied by Apitz-Castro et al., and it is expected that ajoene will be a potent preventive and curing agent of thrombosis, arteriosclerosis, hyperlipemia or other circulatory diseases. Tadi et al. reported that ajoene inhibits the interaction between aflatoxin B.sub.1 (one of the strongest known carcinogens) and DNA. Scharfenberg et al. also found that ajoene has cytotoxic effect on tumor cells. Furthermore, the anti-eumycetes and antifungal actions of ajoene were reported by Yoshida et al. Its antiviral effects were reported by Weber et al. and some anti-AIDS effects were reported by Tatarintsev et al. Ajoene provides the same degree of antibacterial and antifungal effect as 5-fluorocytosine, and is expected as an antibacterial and antifungal agent.
Ajoene, having the aforementioned strong effects, is not found in natural garlic. It is known that ajoene is formed by polymerization of decomposed products of allicin, which is formed by enzymatic decomposition of alliin (sulfur-containing substance) with aliinase, under some specific conditions.
Lawson et al. (Planta Medica 57, P363-370, 1991) investigated many garlic health foods in the world and reported that he found ajoene only in vegetable oil macerated garlic products. However, the ajoene content he reported is as little as 60 to 148 .mu.g/g product, and the content of Z-ajoene having a strong bio-activity in the total ajoenes is only 50% or less.
Regarding the method of preparing ajoene, it is disclosed in Japanese Laid-open Patent Application No. 62-129224 that when garlic is heated to 40.degree.-90.degree. C. in ethyl alcohol, methyl alcohol or other organic solvent having an acidity of pH 2-6 ajoene is obtained.
In the processing method using the aforementioned organic solvent, only a slight amount, about 900 .mu.g of ajoene per 1 kg of garlic is obtained. To obtain the necessary amount of ajoene, a large amount of garlic is required. When ajoene is produced with such a processing method for utilization in foods and drugs, some processes such as the removal of solvent, refinement and so on, complicate the process steps of the method. Moreover, in the above-mentioned method, only a small amount of Z-ajoene, that has a strong bio-activity on inhibition of platelet aggregation and antibacterial and antifungal activities, is obtained.